The oyster traditionally referred to as Booneostrea subucula (Jousseaume in Lamy, 1925) exemplifies persistent generic instability in Ostreinae, driven by misidentified type material and debated synonymies spanning multiple genera, subfamilies and even families. We reassessed the identity of Ostrea subucula and the validity of Booneostrea Harry, 1985 using an integrative approach that combined shell morphology, anatomy and multilocus phylogenetic data. Phylogenetic analyses reveal two deeply divergent, reciprocally monophyletic lineages. The Western Indian Ocean lineage corresponds to O. subucula sensu stricto and ranges from Rodrigues to Yemen and Oman. By contrast, the northern Arabian-Persian Gulf lineage represents a distinct species, here described as Ostrea sorosubucula sp. nov. Despite substantial genetic divergence, morphological differences are subtle, mainly in the adductor muscle scar. Re-examination of historical material reveals that the type concept of Booneostrea is based on misidentified or now-untraceable shells. Ostrea subucula and Ostrea setoensis Habe, 1958 are morphologically and genetically distinct, and O. subucula does not conform to the shell features historically used to define Booneostrea. We conclude that Booneostrea cannot be applied in a taxonomically consistent and meaningful way and should be treated as a nomen dubium. By resolving this long-standing confusion and documenting an endemic Gulf lineage, this study significantly contributes to stabilising generic concepts in Ostreinae and demonstrates the power of integrating molecular and morphological evidence in oyster systematics. ZooBank: urn:lsid:zoobank.org:pub:ECDB3E11-0C17-4EE9-A253-36EC59B28DD8.

Symbiotic relationships are ubiquitous across nature and play key roles in the maintenance of biodiversity and ecosystem function. The Myzostomida are an enigmatic clade of marine annelids that live as obligate symbionts on or inside their predominantly echinoderm hosts. Species of myzostomid have diverse morphologies and lifestyles, ranging from cyst and gall forming, to parasitic host eating, and free-living ectocommensalism. Largely described from shallow tropical waters, there is currently limited information on myzostomids from the deep sea. Here we describe, using integrated morphological and molecular data, the first genus and two species of myzostomid from the abyssal seafloor, found living ectocommensally on porcellanasterid starfish from 3490 to 4362m deep in the central and North Pacific Ocean. Molecular phylogenetic analyses using both nuclear (18S rRNA, H3) and mitochondrial (COI, 16S rRNA) markers recovered Myrmekimyzostomumgen. nov. as monophyletic, and the sole commensal genus in a clade of parasitic species associated with asteroids and ophiuroids. Trait-mapping across the phylogeny suggests the ancestral myzostomid form likely lived ectocommensally on stalked crinoids, with parasitism emerging multiple times in their evolutionary history. These new taxa underline the substantial ecological and evolutionary novelty that can be found in the deep sea. Zoobank: urn:lsid:zoobank.org:pub:332B8B95-F390-4D9F-B1FE-E9E4D433E24C.

Reports of cryptic species have increased in recent decades, driven by advances in molecular studies and accessibility of DNA sequencing, resulting in integrative taxonomy as the standard for species description. This is especially evident in environments where sampling is difficult, such as the deep-sea. Specimens belonging to the subfamily Gymnonereidinae were collected from various deep-water habitats in Brazil. Initial morphological analysis divided them into two morphotypes belonging to the genera Micronereides and Ceratocephale. However, species delimitation using the COI genetic marker revealed the presence of seven distinct species, suggesting the existence of cryptic species complexes within each morphotype, where species are morphologically indistinguishable. Three species recovered in the analyses belong to the genus Micronereides and are morphologically indistinguishable from the type species Micronereides capensis, previously reported in Brazilian deep waters. The lack of molecular data on the type M. capensis hampers the description of these new species. We, therefore, suggest the existence of the Micronereides capensis cryptic complex. Similarly, the Ceratocephale cryptica cryptic complex encompasses the remaining four species identified in this study. Among them, only Ceratocephale cryptica sp. nov. is formally described here. This study provides strong support for the validity of the genus Micronereides, which was questioned in previous studies. Cryptic speciation processes are further discussed, comparing evolutionary divergence rates of the different genetic markers used for phylogenetic inference. These results highlight the challenges of deep-sea species delimitation, calling for revised biodiversity assessments and more complete genetic databases, especially including type species sequences, and at the same time reinforcing the critical role of integrative taxonomy in revealing cryptic diversity. ZooBank: urn:lsid:zoobank.org:pub:8FFA8C17-DFF5-44D3-B343-ABD8E45C62CD.

Taxonomic decisions are critically dependent on the reliability of the analysed characters. However, when character conflicts arise, such as discrepancies between shell morphology and molecular data, relying solely on prior assumptions about the systematic significance of characters and taxa can lead to erroneous conclusions. This is because inductive reasoning, unlike deduction, produces probabilistic rather than definitive conclusions. The uncertainty inherent in induction stems from the incompleteness of our observations; thus, using a partial or selective dataset increases the likelihood of error. To address this issue, we conducted a case study using the genus Cathaica. First, we reconstructed molecular phylogenies based on all available published datasets. Next, we performed discrete and continuous character optimisations to identify apomorphic characters. Finally, we explored the correlation between molecular distances and shell morphological distances. Our character optimisation revealed that shell characters are highly variable and often discordant with molecular data, whereas discrete genital characters exhibit stronger congruence with phylogenetic relationships. Notably, molecular distances were not significantly correlated with shell landmark Euclidean distances, underscoring the mismatch between genetic and shell-based evidence. Based on these findings, we propose that C. zhangcunxiangi, C. wangjiaxunae and C. sculptilis are synonyms of C. fasciola, and C. mengi is a synonym of C. pyrrhozona. This study emphasises that relying solely on partial datasets or untested characters, without considering the probabilistic nature of non-deductive inference, can lead to misleading taxonomic interpretations.

This paper updates the systematics of Aeolidiidae (Heterobranchia, Nudibranchia), with special emphasis on the genus Aeolidiella Bergh, 1867. Up to now, Aeolidiella was composed of five valid species: A. alderi, A. glauca, A. rubra, A. sanguinea from the Mediterranean Sea and the Eastern Atlantic and A. drusillacomb. nov. from the Pacific Ocean. To clarify the systematics of this genus we present an integrative approach based on molecular and morphological data, literature review, species delimitation approaches, and haplotype network analysis. Aeolidiella glauca was recognized as a species complex resulting in the description of Aeolidiella avatarsp. nov., whereas the nominal name A. rubra is considered nomem dubium. The species Aeolidiella drusillacomb. nov. is ascribed to the new genus Novaeolidiellagen. nov. together with the new species Novaeolidiella janaesp. nov. from the Philippines. This restricts the genus Aeolidiella to the Atlantic Ocean and Mediterranean Sea. ZooBank: urn:lsid:zoobank.org:pub:2A14F139-675B-4079-B908-B5EBA20F36E3.

The genus Rhytisma Alderslade, 2000 (Octocorallia: Malacalcyonacea: Lemnaliidae), formerly comprising four nominal species (R. fulvum, R. fuscum, R. monticulum and R. rubiginosum), is revised using an integrative approach. We combine morphological and phylogenomic data for newly collected and historical specimens. A neotype is designated for R. fulvum and a lectotype for R. fuscum to stabilise the application of these names. Six new species are described from the Indo-Pacific: R. acoronatum sp. nov., R. calyaceum sp. nov., R. oblongum sp. nov., R. inaequale sp. nov., R. karibu sp. nov. and R. sperkolae sp. nov. Species delimitation is supported by discrete combinations of morphological characters - particularly those of the tentacle and polyp sclerites - as well as multi-locus DNA barcoding and phylogenomic analyses of conserved elements (UCE and exon loci). Our findings highlight the diagnostic value of tentacle sclerites and reveal extensive species-level diversity that was previously obscured by insufficient morphological examination. The revised genus currently comprises 10 valid species, many of which display restricted geographic distributions, reflecting patterns of regional endemism in Indo-Pacific octocoral assemblages. These results underscore the importance of integrative taxonomy in uncovering hidden biodiversity. ZooBank: urn:lsid:zoobank.org:pub:3CFB17F3-F571-4B5E-9B83-93FFB0B915B3.

We present the most comprehensive revision to date of the Neotropical false dragon millipede tribe Cornalatini Verhoeff, 1941. We (1) test the monophyly of Cornalatini through a morphology-based cladistic analysis; (2) conduct the first molecular study to extensively sample Chelodesmidae across multiple taxa and gene regions in a phylogenetic context; and (3) revise the taxonomy of the tribe. Our morphology-based phylogenetic analysis, in which 56 morphological characters were scored across 11 ingroup and 9 outgroup terminals, recovered 6 synapomorphies supporting the monophyly of the tribe and providing the basis for a revised classification of the group. In addition, we provide the first molecular analysis of Chelodesmidae, based on the nuclear EF1α gene, including six ingroup and four outgroup species, and discuss implications for future phylogenetic studies of the family. Based on our results, we include within Cornalatini the genera Cornalatus Attems, 1931, Leodesmus Mauriès & Geoffroy, 2000, Obiricodesmus Schubart, 1955, Pseudoleptodesmus Brölemann, 1902, and the newly proposed genera Monidracodesmusgen. nov. and Pseudodracodesmusgen. nov. We also describe three new species for the tribe, Leodesmus acutussp. nov. and Leodesmus alambarisp. nov. from limestone caves in São Paulo state, Brazil, and Monidracodesmus maysp. nov. from forested habitats in Bahia state, Brazil. We recognize Cornalatus tabulus Hoffman, 1990 as a junior synonym of Cornalatus permutatus (Attems, 1938), and Obiricodesmus terrigena (Attems, 1943) and Obiricodesmus brasiliae (Brölemann, 1902) as junior synonyms of Obiricodesmus rosascens (Brandt, 1839). Our study clarifies the taxonomy of Cornalatini and provides a solid framework for future studies of Chelodesmidae. ZooBank: urn:lsid:zoobank.org:pub:1D7C09AC-DA1D-4453-BA5D-5F2A28501FD5.

Kanaky | New Caledonia is an exceptional biodiversity hotspot, home to a vast number of endemic lineages including many invertebrate groups. We investigate a relatively understudied radiation of Zalmoxidae (Arachnida, Opiliones) in Kanaky, with the aim of determining whether the rich diversity stemmed from a single or multiple colonization event(s). To do so we assembled the first genomic-scale dataset of this family, with particular focus on the Kanaky lineages, using ultra-conserved element (UCE) sequencing techniques. We find evidence for monophyly of the Kanaky zalmoxids, suggesting that there was a single colonization of the archipelago from neighboring lineages in the South Pacific. We further document explosive evolution of Zalmoxis on the archipelago, comparing it with prior taxonomic work on the family and finding a plethora of novel forms. There is a clear need for greater sampling and systematic study of this highly diverse clade of archipelagic harvesters.

Lebbeus White, 1847 is the most diverse and widespread genus in the caridean family Thoridae Kingsley, 1879. Species of the genus have adapted to various habitats, inhabiting from shallow to deep water (>3000m), low latitudinal to polar regions, and with free-living to symbiotic lifestyles. In spite of recent studies, the phylogenetic position of Lebbeus within Thoridae and its internal phylogenetic relationships remain to be explored. In this study, three new species of Lebbeus recently collected from deep water in the Philippine Sea are described using an integrative taxonomic approach. The new species are formally named Lebbeus chunshengisp. nov., Lebbeus lizheisp. nov., and Lebbeus xinzhengisp. nov. herein. The molecular phylogenetic analyses led the authors to revise the internal grouping of Lebbeus, which has long been relied on the development of the pereopodal epipods. It has been clarified that characters derived from the rostrum and carapace better reflect the phylogeny, and this finding prompted us to propose four informal species groups within Lebbeus. Additionally, we tentatively uncovered the phylogenetic position of Lebbeus by reconstructing a backbone phylogeny of Thoridae based on genome-skimming sequencing data. Our phylogeny supports the recent divergence of Lebbeus and its sister-group relationship with Spirontocaris Spence Bate, 1888. However, more extensive taxon sampling is needed to elucidate the monophyly of each thorid genus. This work provides critical baseline data for the conservation and restoration of habitats in the region, and advances our understanding of the diversity of sponge-associated shrimps in deep-sea ecosystems of the Western Pacific. ZooBank: urn:lsid:zoobank.org:pub:F6B8185D-CCD5-45AE-850E-24A40B0B20AD.